Heat sink mounted on a vehicle-transmission case

ABSTRACT

A system for dissipating heat from a semiconductor board includes a first substrate including an opening formed therein, a second substrate attached to a surface of the first substrate, and a microchip positioned in the opening and bumped to the second substrate. The system further includes a heat sink directly adhered to the microchip. A method of manufacturing a heat dissipating semiconductor board includes forming an opening in a first substrate and positioning a microchip in the opening. The method further includes directly adhering the microchip to a heat sink, bonding the microchip to a second substrate and boding a surface of the first substrate to the second substrate.

TECHNICAL FIELD OF THE INVENTION

The present invention related generally to thermal dissipation frommicrochips and in particular to thermal dissipation in chip substrates.

BACKGROUND OF THE INVENTION

Heat generation is an undesired byproduct of operating microchips.Typically, excess heat flows to a heat sink through thermal vias andwire bonds. However, as wiring systems become more complex, designersare increasingly being challenged to place the thermal vias, especiallyin applications with limited space. These problems are exacerbated inhigh temperature operating environments. While simple components such asFETS, diodes and low power integrated chips (IC) have solutions,problems exist for high pincount devices such as microchips, flashmemory, SRAM, etc.

Thus, in automotive engine applications, such as automotivetransmissions, designers face a daunting challenge. In such anenvironment, often approaching 140 Celsius, the maximum operatingtemperature can be as low as 150 Celsius, leaving a window of only 10Celsius. While cooling systems can help alleviate these problems, suchsystems add both cost, as well as weight, to the system, and cantherefore be undesirable.

FIG. 1 illustrates a prior art circuit board 100 including substrate105. A plurality of flip chips. IC's and other electronic devices 140are mounted to substrate 105 using appropriate techniques. In addition,microchip 110 is wirebonded 120 to the substrate, with wirebond 120providing at least some heat sink functionality for microchip 110. Ascan be seen in FIG. 1, microchip 110 includes a significant footprint onthe substrate 105, especially when including the wirebond 120.

Therefore, it would be desirable to provide a system for dissipatingheat that would overcome the aforementioned and other disadvantages.

SUMMARY OF THE INVENTION

One aspect of the invention provides a system for dissipating heat froma semiconductor board includes a first substrate including an openingformed therein, a second substrate attached to an upper surface of thefirst substrate, and a microchip positioned in the opening and bumped tothe second substrate. The system further includes a heat sink directlyadhered to the microchip.

Another aspect of the invention provides method of manufacturing a heatdissipating semiconductor board includes forming an opening in a firstsubstrate and positioning a microchip in the opening. The method furtherincludes directly adhering the microchip to a heat sink, bonding themicrochip to a second substrate and bonding a surface of the firstsubstrate to the second substrate.

Yet another aspect of the invention provides a system for dissipatingheat from a semiconductor board includes a first substrate including anopening formed therein, a second substrate attached to an upper surfaceof the first substrate, and a microchip positioned in the opening andbumped to the second substrate. The system further includes a mean fordirectly adhering a microchip to the heat sink.

The foregoing and other features and advantages of the invention willbecome further apparent from the following detailed description of thepresently preferred embodiments, read in conjunction with theaccompanying drawings. The detailed description and drawings are merelyillustrative of the invention, rather than limiting the scope of theinvention being defined by the appended claims and equivalents thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of a first substrate in accordancewith the prior art;

FIG. 2 illustrates an embodiment of a system for thermal dissipation, inaccordance with an aspect of the invention;

FIG. 3 illustrates one embodiment of a method for manufacturing a heatdissipating semiconductor board, in accordance with one aspect of theinvention;

FIG. 4 illustrates one embodiment of a method for manufacturing a heatdissipating semiconductor board, in accordance with one aspect of theinvention;

FIG. 5 illustrates one example of space saved on a board, in accordancewith the teachings of the invention; and

FIG. 6 illustrates an embodiment of a heat sink for thermal dissipation,in accordance with an aspect of the invention.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 2 illustrates one embodiment of a system 200 for thermaldissipation in accordance with one aspect of the invention. System 200includes heat sink 270, microchip 280 and first substrate 240. Firstsubstrate 240 includes an opening 245 formed within first substrate 240.Microchip 280 and first substrate 240 are bumped to second substrate 235with bumps 225. First substrate 240 can be a low density ceramic boardor a Flame Resistant 4 (“FR-4”) board, among other appropriatestructures. Second substrate 235 can be a High Density Interconnection(“HDI”) board, Low Temperature Co-fired Ceramic (“LTCC”) board, or aceramic board, among other appropriate structures. Alternatively, thefirst substrate and second substrate can be the same type of board, suchas HDI, LTCC, Fr-4, ceramic, low density ceramic, or the like.

Additionally, at least one electronic device, such as integrated chip210 and flip chip 220 can be operatively attached to second substrate235. Operative attachment can be made by any appropriate joiningtechnique, such as bumping, soldering, or a direct connection. Anyappropriate material can be used for bumping in accordance with thisdisclosure, including gold and solder. In one embodiment, at least onechip is bumped to the second substrate on a first side of the secondsubstrate, and the microchip is bumped to the second substrate on asecond side of the second substrate, with the first side opposing thesecond side. In such embodiments, the chips and microchip are mounted toopposing sides of the second substrate, such that the microchip can bedirectly mounted to the heat sink with a high thermal conductivityadhesive. Any appropriate devices can be used to bump, such as the K&SWaferPro III Stud Bumper. Chips can be bonded to the first substrate orsecond substrate with the UltraSonic FCX501 FlipChip Bonder, availablefrom Panasonic.

Heat sink 270 is any structure to which heat will flow from theoperative electronic components such as chips 210, 220 and microchip280. In one embodiment, heat sink 270 is a structure made of aluminum.In one embodiment, heat sink 270 is a transmission case. In anotherembodiment, heat sink 270 is directly attached to a transmission case.In one embodiment, heat sink 270 includes at least one ridge sized tofit within opening 245. FIG. 6 illustrates ridge 675 on heat sink 270.In other embodiment, heat sink 270 includes fins or other physicalcharacteristics to increase surface area or improve heat flow.

In one embodiment, first substrate 240 is isolated from heat sink 270 bya low thermal conductivity adhesive 260, such as an adhesive with athermal conductivity of less than approximately 0.9 W/m-K. In oneembodiment, heat sink 270 is directly adhered to microchip 280 with ahigh thermal conductivity adhesive 255, wherein the high thermalconductivity adhesive 255 conducts greater than approximately 2.5 W/m-K.

FIG. 3 illustrates one embodiment of a method 300 for manufacturing aheat dissipating semiconductor board, in accordance with one aspect ofthe invention. Method 300 begins at 305.

At step 310, method 300 forms an opening, such as opening 245, in afirst substrate, such as first substrate 240. The opening can besubstantially circular, polygonal, or any other appropriate shape. Inone embodiment, the opening is sized to accommodate a microchip. In oneembodiment, the opening is sized to accommodate a microchip with a gapbetween the microchip and the first substrate. In some embodiments, thegap can be filled with underfill, depending on design. The opening canbe created by dicing the substrate, or by attaching a plurality ofsubstrates together to define the opening. A microchip is bonded to thesecond substrate at step 320 and the microchip is positioned in theopening at step 330. The microchip is then directly adhered to a heatsink at step 340. In one embodiment, a high thermal conductivityadhesive adheres the microchip to the heat sink. The second substrate isbonded to the first substrate at step 350. Method 300 ends at step 395.

FIG. 4 illustrates one embodiment of a method 400 for manufacturing aheat dissipating semiconductor board, in accordance with one aspect ofthe invention. Method 400 begins at 405.

At step 410, method 400 forms an opening, such as opening 245, in afirst substrate, such as first substrate 240. The opening can besubstantially circular, polygonal, or any other appropriate shape. Inone embodiment, the opening is sized to accommodate a microchip. In oneembodiment, the opening is sized to accommodate a microchip with a gapbetween the microchip and the first substrate. In some embodiments, thegap can be filled with underfill, depending on design. The opening canbe created by dicing the substrate, or by attaching a plurality ofsubstrates together to define the opening. A microchip is bonded to thesecond substrate at step 420 and the microchip is positioned in theopening at step 430. The microchip is then directly adhered to a heatsink at step 440. In one embodiment, a high thermal conductivityadhesive adheres the microchip to the heat sink. The second substrate isbonded to the first substrate at step 450.

At least one chip is bumped to the second substrate at step 415. Thechip is bumped to a first side of the second substrate (such as the topside) while the microchip is bumped to a second side of the secondsubstrate (such as the bottom side), and the first side of the secondsubstrate opposes the second side of the second substrate.

Method 400 ends at step 495.

Use of this disclosure enables both improved heat flow from themicrochip to the heat sink, and also design of bare dies to be mountedon LTCC boards. Removal of heat spreaders saves both space and cost.Higher power items like a microprocessor, would be stud bumped to thebottom of a small HDI/LTCC board and the die would be thermally attachedto the baseplate with high conductivity adhesive. Lower powercomponents, such as IC's and flip chips can be attached to the top ofthe small substrate, with thermal vias for heat transfer as needed. Thiskeeps the bottom available for signal I/O balls and allows the substrateto remain small. Higher density is achieved by using IC's as flip chipson both sides of the board, and solder balls, would be the interconnectto the large substrate, similar to a BGA.

In addition to functional advantages, the disclosure herein cancontribute to cost advantages as well. For example, high density routingis primarily on the second substrate, so that the larger substrate, i.e.first substrate 240 can be a simpler and less costly design. Replacinggold wirebonding with gold stud bumping will reduce costs due to lessmaterial and higher throughput and no outsourced flip chip logisticalissues.

For example, an application of the teaching to the board depicted inFIG. 1 could result in a board space savings of 0.532 in² out of 4.58in², FIG. 5 illustrates another board featuring significant spacesavings, wherein the white areas 502 represent saved space from the lackof wirebonding surrounding the wirebonded microchip.

While the teachings of this disclosure are applicable in any operatingenvironment, it is anticipated that one operating environment isautomotive, especially in a transmission or engine controller. Thus, themicrochip can be a chip including instructions for operating atransmission. Alternatively, the microchip can be a chip includinginstructions for operating an engine.

It is important to note that the figures and description illustratespecific applications and embodiments of the present invention, and isnot intended to limit the scope of the present disclosure or claims tothat which is presented therein. Upon reading the specification andreviewing the drawings hereof, it will become immediately obvious tothose skilled in the art that myriad other embodiments of the presentinvention are possible, and that such embodiments are contemplated andfall within the scope of the presently claimed invention.

While the embodiments of the invention disclosed herein are presentlyconsidered to be preferred, various changes and modifications can bemade without departing from the spirit and scope of the invention. Thescope of the invention is indicated in the appended claims, and allchanges that come within the meaning and range of equivalents areintended to be embraced therein.

1. A system for dissipating heat from a semiconductor board, comprising:a first substrate including an opening formed therein; a secondsubstrate attached to a surface of the first substrate; a microchippositioned in the opening and bumped to the second substrate; a heatsink directly adhered to the microchip; a transmission case, and theheat sink is integral with the transmission case; and at least one ridgeformed as part of the heat sink, the at least one ridge sized to fitwithin the opening.
 2. The system of claim 1 wherein the first substrateis FR-4 board.
 3. The system of claim 1 wherein the first substrate is alow density ceramic board.
 4. The system of claim 1 wherein the secondsubstrate is a HDI board.
 5. The system of claim 1 wherein the secondsubstrate is a Low Temperature Co-fired Ceramic board.
 6. The system ofclaim 1 wherein the second substrate is a ceramic board.
 7. The systemof claim 1 wherein the heat sink adheres to the microchip with a highthermal conductivity adhesive, wherein the high thermal conductivityadhesive has a conductivity greater than 2.5 W/m-K.
 8. The system ofclaim 1 further comprising at least one chip bumped to the secondsubstrate, wherein the at least one chip is bumped to the secondsubstrate on a first side of the second substrate, and wherein themicrochip is bumped to the second substrate on a second side of thesecond substrate, and wherein the first side of the second substrateopposes the second side of the second substrate.
 9. The system of claim1 wherein the heat sink adheres to the first substrate with a lowthermal conductivity adhesive, wherein the low conductivity adhesive hasa conductivity less than 0.9 W/m-K.
 10. The system of claim 1 whereinthe bumps are gold bumps.
 11. The system of claim 1 wherein the bumpsare solder bumps.
 12. The system of claim 1 wherein the microchipincludes instructions for operating a transmission.
 13. The system ofclaim 1 wherein the microchip includes instructions for operating anengine.
 14. A method of manufacturing a heat dissipating semiconductorboard, the method comprising: forming an opening in a first substrate;bonding a microchip to a second substrate; positioning the microchip inthe opening; directly adhering the microchip to a heat sink; bonding asurface of the first substrate to the second substrate; mounting theheat sink on a transmission case, the heat sink having at least oneridge sized to fit within the opening.
 15. The method of claim 14further comprising: bumping at least one chip to the second substrate,wherein the at least one chip is bumped to the second substrate on afirst side of the second substrate, and wherein the microchip is bumpedto the second substrate on a second side of the second substrate, andwherein the first side of the second substrate opposes the second sideof the second substrate.
 16. A system for dissipating heat from asemiconductor board, comprising: a first substrate including an openingformed therein; a second substrate attached to an upper surface of thefirst substrate; a microchip positioned in the opening and bumped to thesecond substrate; means for adhering a heat sink directly to themicrochip; and means for mounting the heat sink on a transmission case,such that at least one ridge formed as part of the heat sink is sized tofit within the opening.